2 files changed, 15 insertions, 5 deletions

diff --git a/crates/ra_analysis/src/imp.rs b/crates/ra_analysis/src/imp.rs
index a67b1717a..3a135ef13 100644
--- a/crates/ra_analysis/src/imp.rs
+++ b/crates/ra_analysis/src/imp.rs
@@ -20,7 +20,7 @@ use crate::{
     descriptors::{FnDescriptor, ModuleTreeDescriptor, Problem},
     roots::{ReadonlySourceRoot, SourceRoot, WritableSourceRoot},
     CrateGraph, CrateId, Diagnostic, FileId, FileResolver, FileSystemEdit, JobToken, Position,
-    Query, SourceChange, SourceFileEdit,
+    Query, SourceChange, SourceFileEdit, Cancelable,
 };
 
 #[derive(Clone, Debug)]
@@ -157,10 +157,10 @@ impl AnalysisImpl {
         }
         query.search(&buf, token)
     }
-    pub fn parent_module(&self, file_id: FileId) -> Vec<(FileId, FileSymbol)> {
+    pub fn parent_module(&self, file_id: FileId) -> Cancelable<Vec<(FileId, FileSymbol)>> {
         let root = self.root(file_id);
         let module_tree = root.module_tree();
-        module_tree
+        let res = module_tree
             .parent_modules(file_id)
             .iter()
             .map(|link| {
@@ -174,7 +174,8 @@ impl AnalysisImpl {
                 };
                 (file_id, sym)
             })
-            .collect()
+            .collect();
+        Ok(res)
     }
     pub fn crate_for(&self, file_id: FileId) -> Vec<CrateId> {
         let module_tree = self.root(file_id).module_tree();
diff --git a/crates/ra_analysis/src/lib.rs b/crates/ra_analysis/src/lib.rs
index b1d5c4936..988a45b46 100644
--- a/crates/ra_analysis/src/lib.rs
+++ b/crates/ra_analysis/src/lib.rs
@@ -42,6 +42,15 @@ pub struct Cancel;
 
 pub type Cancelable<T> = Result<T, Cancel>;
 
+impl std::fmt::Display for Cancel {
+    fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        fmt.write_str("Canceled")
+    }
+}
+
+impl std::error::Error for Cancel {
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct FileId(pub u32);
 
@@ -225,7 +234,7 @@ impl Analysis {
     pub fn find_all_refs(&self, file_id: FileId, offset: TextUnit, token: &JobToken) -> Vec<(FileId, TextRange)> {
         self.imp.find_all_refs(file_id, offset, token)
     }
-    pub fn parent_module(&self, file_id: FileId) -> Vec<(FileId, FileSymbol)> {
+    pub fn parent_module(&self, file_id: FileId) -> Cancelable<Vec<(FileId, FileSymbol)>> {
         self.imp.parent_module(file_id)
     }
     pub fn crate_for(&self, file_id: FileId) -> Vec<CrateId> {